Photo-index cathode ray device



F. P. KEIPER, JR 2,959,682

PHOTO-INDEX cm1-loma RAY DEVICE Filed nec. 17, 195s Nov. 8, 1960 United States Patent CS,

PHOTG-INDEX. CATHODE RAY DEVICEv Francis P. Keiper, Jr., Oreland, Pa., assigner'v tov Philco Corporation, Philadelphia, Pa., a corporation of Penm Sylvania Filed Dec. 17, 1958, Ser. No. 781,106

9 Claims. (Cl. Z50-217);

This invention relates to photo-index type cathode.y ray devices in which indexing signals are produced by electron beam impingement of light-emissive indexing elements and by translation of the emitted light into electrical signals. Such a device is useful, for example,l as the. display device of a color television receiver, in which case; the indexing signals are utilized to ensure proper color rendition. In the preferred form ofv such a display device, the color image-producing elements are in the form of phosphor stripes extending, transversely to the direction of4 line scanning, the stripes being arranged in4 suc-- cessive groups whoseindividual. stripes emit lightofdiifer ent primaryA colors, and the; indexing elements are. inthe. form of stripes parallel to the image-producing stripes.

In the preferred form ofl such a device, the light which. produces the indexing signals is emitted rearwardly from. the cathode ray tube screen within the funnel or. bell portion ofthe tube envelope andA i`s-collected by a phototelecfv tric device suitably arranged to receive the light. y

An improved form of such a cathode raydevice is disclosed in U.S. Patent No.. 2,749,449., issued June 5, 1956, toW. E. Bradley et al., which teaches` the provision of, a`

light` reflect-ing and diiusing surface on the inside of the.

devicet contained within an. opaquev envelope or housing.

adjacent the outside of a window in said-` bell portion. The provisionof the light reecting and diffusingv surface on the inside of said bell portion increases the amount of.` light received by the. photoelectric device. and, thusL in-4 creasesY the amplitude of theindexing signals.

While the structure taught'v in the, Bradley et al. patent represents an important, advance in the art, in practice.. it` has been found that there is still room for improvement in. respect to the amplitude of theindexing signals; in order to assure proper drive of thecorrection control, circuits. Although the` light rellecting andi dilfusing surface of thev Bradley et al. patent causes far less light loss than does. a light-absorbing coating suchA as` the previously used aquadag coating, only a relatively small portion of the light reaches the photoelectric device. This isdue tothe fact that the area of the photocathode, which` is in confronting relation to the aforementioned window, i's small in relationl to ther area of the lightI reflecting and diffusing surface.

Having in'mind that the objective is tol deliver as much. light as possible to thev photocathode of a photoelectric` device such as a photornultiplier tube, the amount of, delivered light could be increased by increasing the area of the normallyplanar. photocathode.. Howeventhis is impractical because it necessitates special construction of the photoelectric device and involves substantial additional cost.

Theprincipalf object ofthe present invention is to pro'- vide a highly satisfactory and practical solution of the problem of delivering an adequate amount of light to the photoelectric device.

Y Patented Nov. 8,y 196()y In; accordance with the present invention, there isV providedy a photo-index cathode ray device employingl the. light reecting; anddiifusing coating of. the Bradley et. al; patentf and. also employing an improved light-collection'l arrangement'. Theflatter comprises al Window in the hell, portion of the cathode ray tube, an envelope or housing. adjacent', the outside: of said window and having a light'v reflecting and. diffusing surface on the inside thereof, and; a. photoelectric device: having a. photocathode within said housing-l in confronting relation to the light reflecting andV diffusing surface of saidr housing to receivel light therefrom. By virtue of this novel structure,V the light delivered to the photocathode surface is greatly increased and is fully adequateY to assure suiiicient amplitude of: the indexing; signals produced by the photoelectric de vice..

Theinventionrnay be fully understood from the following detailed description with reference to the accompany'- ing drawing wherein the single figure is a longitudinalk sectional view of a cathode ray device, for use asV the, dis play device of a color television receiver, embodying oney form of the present invention.

Referring more particularly to the drawing, there is shown acathode rayv tube 10 ofthe character disclosed: inY the aforementioned Bradley et al. patent. The; tube" comprises the usual neck and bell portions 11 and 12, and the usual faceplate 13'` O11 the faceplate there are color triplets, each comprising phosphor stripes 14,Y 15 andA 16, extending transversely to the direction of line scanning andl emissive of light in different primary colors. Placed over thel colored light-emissive stripes is an electron-perf meable light-opaqueiilm 17 which is preferablyl formedrof aluminum. Thescreen thus constituted has on its rear surface. light-emissivey indexing stripes 18 which mayv be, composed of phosphor and which also extend transverselyv to the direction of line scanning. It will be understood` that the1stripes 1'4 to 16l and 18 are not drawn to scale but are merely representative of the screen structure inf which. the` stripes are so multitudinousl and so ne as; to preclude their beingdrawn. to scale.

Onthe inside surface of the bell portion 12,V there is,J provided the reflecting and diifusing surface 19v accord-y ing to the teaching of the Bradley etal. patent. As there- I in described, this surface may be provided by an; elec,- trically conductive coating such as a roughened coating of aluminum or silver, in which case the coating may also serve as. an anode coating, or the coatingv may be a non, conductive coating deposited upon the. anode, such as mightbe provided. by magnesium `oxide crystals. Electrif cal connection is made to the anode coatingY through the exterior connector fitting 20;

It will be understood, of course, that the cathode ray tube also comprises the conventional beam producing4 andl focussing elements with which the present invention is not` concerned and which therefore are not shown.

For collection of the light emitted. by the indexing. elements 18, a window 21 is provided in the bell portion 12 of thek cathode ray tube. provided by this: invention it isn possible, and in fact desirable, to employ a clear glass w-indow which may simplyA com-prise a clear portion of the glass wall 12. The window receives' light fromthe elements 18 both directly and by tliefdifuse reflection of r`eating 19.

In :accordance with the present invention, an envelope'A or housing/22 is provided, adjacent the outside of window` 21', havingalight-reflecting and dilfusing surface 23 on theV inside thereof. This housing mayv be composedof glass, and the surface-.23 may be provided by a coatingof' the. same character asf that'which provides the surface 19. Thus it will be seen that the surface 23 is effectively an extension of the surface 19 external to the envelope Because of the structurey of the cathode ray tube. Further, in accordance with this invention, a photoelectric device 24 is provided having a photocathode 25 within the housing 22 in confronting relation to the light reflecting and diffusing surface 23.

The device 24 may be a conventional head-on photomultiplier tube having its photocathode extended over a portion of its cylindrical wall. As is well known, the conventional head-on photomultiplier comprises a cylindrical glass envelope having an end wall upon which the photocathode surface is provided, an anode within the' envelope, and a plurality of dynode electrodes also within the envelope. Such a tube may be adapted for the purpose of the present invention simply by extending the photocathode along a portion of the cylindrical glass wall.

In such case it will be seen that the photocathode comprises two areas, i.e. the end area in confronting relation to the window 21 and the side area in confronting relation to surface 23. However, if the length of the side area is at least equal to the diameter of the end area, the side area is at least four times as large as the end area. Therefore the side area, in cooperation with surface 23, is much more effective than is the end area, and therein resides the improvement provided by this invention. Moreover the combination of the two has the advantage that the effect of the end area is added to that of the side area.

As shown in the drawing, the photomultiplier tube may extend through an opening in the housing 22. The latter is preferably of hemispherical form, although it may be of any other suitable form.

Alternatively, the photoelectric device may be a photodiode having its photocathode extended over its glass surface.

From the foregoing description, it will be seen that this invention represents an advance in the art beyond the contribution of the aforementioned Bradley et al. patent. Thus this invention has provided a novel structural combination including the reflecting and diffusing surface 19 and the collector arrangement in cooperative association therewith.

While a preferred embodiment of the invention has been illustrated and described, it will be apparent that various modications thereof are possible without departing from the spirit and scope of the invention. It will be understood therefore that the invention is not limited to the illustrated embodiment but contemplates such modifications and further embodiments as may occur to those skilled in the art.

` I claim:

1. A photo-index cathode ray device, comprising a cathode ray tube having an envelope including a bell portion and a screen at the larger end of said bell portion, electron-excitable light-emissive indexing elements on the inside of said screen, a light reflecting and diffusing surface on the inside of said bell portion, a light-transmissive window in said bell portion to receive light from said elements both directly and indirectly by the diffuse reilection of said surface, a housing adjacent the outside of said window to receive light transmitted therethrough, a light reliecting and diffusing surface on the inside wall of said housing, and a photoelectric device having a photocathode within said housing in confronting relation to the last-mentioned surface, whereby said photocathode receives light transmitted through said window by the diffuse reflection of the last-mentioned surface.

2. A photo-index cathode ray device according to claim l, wherein said housing is substantially of hemispherical form.

3. A photo-index cathode ray device, comprising a cathode ray tube having an envelope including a bell portion and a screen at the larger end of said Ybell portion, electron-excitable light-emissive indexing elements on the inside of said screen, a light reflecting Iand diffusing surface on the inside of said bell portion, a light-transmissive window in said bell portion to receive light from said elements both directly and indirectly by the diffuse reflection of said surface, a housing adjacent the outside of said window to receive light transmitted therethrough, a light reflecting and diffusing surface on the inside wall of said housing, and a photoelectric device having a photocathode within said housing in confronting relation both to said window and to the last-mentioned surface, whereby said photocathode receives light transmitted through said window both directly and indirectly by the diffuse reflection of the last-mentioned surface.

4. A photo-index cathode ray device according to claim 3, wherein said photo electrode device is of cylindrical form, and said photocathode extends over an end surface and at least a portion of the cylindrical wall.

5. A color television display device, comprising a cathode ray tube having an envelope including a bell portion and a screen at the larger end of said bell portion, said screen comprising both forwardly and rearwardlypresented light-generating elements separated by a thin electron-transparent light-opaque layer, a light reflecting and diffusing surface on the inside of said bell portion, a light-transmissive window in said bell portion to receive light from the rearwardly-presented elements both directly and by the diffuse refiection of said surface, a housing adjacent the outside of said window to receive light transmitted therethrough, a light reflecting and diffusing surface on the inside wall of said housing, and a photoelectric device having a photocathode within said housing in confronting relation to the last-mentioned surface, whereby said photocathode receives light transmitted through said window indirectly by the diffuse reflection of the lastmentioned surface.

6. A color television display device according to claim 5, wherein said housing is substantially of hemispherical form.

7. A color television display device, comprising a cathode ray tube having an envelope including a bell portion and a screen at the larger end of said bell portion, said screen comprising both forwardly and rearwardlypresented light-generating elements separated by a thin electron-transparent light-opaque layer, a light reflecting and diffusing surface on the inside of said bell portion, a light-transmissive window in said bell portion to receive light from the rearwardly-presented elements both directly and by the diffuse reflection of said surface, a housing adjacent the outside of said window to receive light transmitted therethrough, a light reflecting and diffusing surface on the inside wall of said housing, and a photoelectric device having a photocathode within said housing in confronting relation both to said window and to the last-mentioned surface, whereby said photocathode receives light transmitted through said window both directly and indirectly by the diffuse reflection of the lastmentioned surface.

8. A color television display device according to claim 7, wherein said photoelectric device is of cylindrical form, and said photocathode extends over an end surface and at least a portion of the cylindrical wall.

9. A color television display device according to claim 8, wherein the length of the photocathode area on said cylindrical wall is at least equal to the diameter of said end surface, whereby the photocathode area on said cylindrical surface is at least four times as large as the photocathode area on said end surface.

References Cited in the file of this patent UNITED STATES PATENTS 

